Tension-force coupled high-pressure pumping

ABSTRACT

A pumping apparatus ( 200 ) for delivering liquid at a high pressure (Psys) at which compressibility of the liquid becomes noticeable, comprises a piston ( 20 ) adapted for reciprocation in opposing directions in a pump working chamber ( 30 ), and a drive ( 40 ) coupled to the piston ( 20 ) to apply a tension force onto the piston ( 20 ) in order to move the piston ( 20 ) into a drive direction ( 50 ).

BACKGROUND ART

The present invention relates to delivering liquid at a high pressure atwhich compressibility of the liquid becomes noticeable.

FIG. 1 illustrates a typical example of a pump 10, as known in the art,for delivering liquid at a high pressure at which compressibility of theliquid becomes noticeable. An example of such pump 10 is disclosed e.g.in EP 0309596 A1.

The pump 10 comprises a piston 20 reciprocating in opposing directionsin a pump working chamber 30. A drive 40, e.g. a spindle drive as in theaforementioned EP 0309596 A1, is coupled to the piston 20 and applies apressure force in a direction as indicated by arrow 50, in order to movethe piston into the direction 50, thus decreasing a pump volume 60. Thepump volume 60 is usually provided by the volume between the piston 20and the pump working chamber 30 and usually further includes the volumeof the working chamber 30 up until an inlet valve 70 and/or an outletvalve 80. The pump volume 60 is usually further defined by a drive seal90 applied for sealing the pump working chamber against or in thedirection of the drive 40.

A return mechanism 100, which can be e.g. a spring mechanism, is usuallyprovided and coupled to the piston 20 for counteracting against themovement of the piston 20 into the drive direction 50. Once the piston20 reaches its top dead center, i.e. when the pump volume 60 isminimized, the return mechanism 100—usually in combination with thepressure in the pump working chamber 30—moves the piston 20 in a returndirection 55 opposite to the drive direction 50. Thus, the pump volume60 is increased during the movement into the return direction.

The movement of the piston 20 into the drive direction 50 is usuallyprovided to compress the liquid in the pump working chamber 30.Dependent on the settings of the valves 70 and 80, the compression ofthe liquid during movement into the drive direction 50 is usually donein order to provide a system pressure Psys at an outlet 110 of the pump10. Movement of the piston 20 into the return direction 55 is usuallyprovided to fill the pump working chamber 30 with liquid provided at aninlet 120 of the pump 10. The inlet 120 might be coupled to a liquidreservoir (usually at ambient pressure) or to another pump for supplyingthe liquid. This is indicated in FIG. 1 by a liquid supply 130 supplyingthe liquid to the pump 10 at a pressure Psup.

DISCLOSURE

It is an object of the invention to provide an improved delivering ofliquid at a high pressure at which compressibility of the liquid becomesnoticeable. The object is solved by the independent claim(s). Furtherembodiments are shown by the dependent claim(s).

Embodiments according to the present invention provide a pumpingapparatus for delivering liquid at a high pressure at whichcompressibility of the liquid becomes noticeable. The pumping apparatuscomprises a piston for reciprocating in opposing directions in a pumpworking chamber. A drive is coupled to the piston in order to apply atension force onto the piston in order to move the piston into a drivedirection.

The tension force coupling between the drive and the piston allowsproviding an easier design of the mechanical alignment of the piston inthe pump working chamber with respect to the pressure force coupling asillustrated in FIG. 1. The pressure coupled drive in FIG. 1 requires avery sophisticated design of the lateral guidance of the piston in theworking chamber, since the piston has a tendency to swerve in adirection perpendicular to the direction of movement under theapplication of the pressure force from the drive. The application of aforce coupling between the piston and the drive, as in embodiments ofthe present invention, reduces the requirements for lateral guidance ofthe piston, thus leading to a less complex and usually less costlydesign together with a reduced abrasion in particularly for the sealing.

A piston which is moved (pushed) by pressure coupling usually has toprovide certain bending resistance and requires a very precise lateralguidance. This typically limits the applicable length and thus thediameter to length ratio. The lateral guiding has to be narrow and/orlong, so that the piston cannot swerve in lateral direction. Thisrequires tight tolerances and leads to friction and abrasion. Sealingsusually have to be quite hard to cover lateral forces resulting fromswerving of the piston. At the same time, such seal(ing)s have to beelastic to ensure the sealing quality.

Using tension coupling of the piston allows overcoming at least some ofthe constraints of pressure coupled pistons. The requirements on lateralguidance are limited since swerving can be reduced, thus also allowingto use different seal(ing)s with lower requirements to hardness.Further, different materials may be used and the applicable lengthand/or diameter to length ratio can be improved.

In one embodiment, a return seal is provided for sealing liquid in thepump working chamber against a return mechanism provided forcounteracting against the movement of the piston. The return mechanismis preferably also coupled to the piston and adapted to move the pistoninto a return direction opposite to the drive direction as provided bythe drive. The return mechanism might also be tension force coupled tothe piston to apply a tension force into the return direction.

The pumping apparatus might further comprise a drive seal for sealingthe pump working chamber against the drive. The drive seal might beprovided in the pump working chamber, so that the piston abuts to thedrive seal in order that liquid is retained in the pump volume of thepump working chamber and prohibited from leaving the pump volume intothe direction of the point of application of the drive.

While the pumping apparatus of FIG. 1 usually requires only the driveseal, embodiments according to the present invention might require suchreturn seal, which might be provided alternatively or in addition to thedrive seal, in order to seal the pump volume at the point of applicationof the return mechanism.

The drive seal and/or the return seal can be embodied e.g. by springassisted PTFE (Polytetrafluorethylen) based polymeric seals, or anyother high pressures sealing has known in the art.

In one embodiment the pump volume is increased when the piston is movedinto the drive direction by the drive tension force coupled to thepiston. Accordingly, the pump volume is than decreased when the pistonis moved into the return direction.

In one embodiment, the piston is coupled on both ends a respectivedrive, each applying tension force onto the piston to move (pull) thepiston in a respective direction.

In order to provide a unidirectional flow of the liquid, one or morevalves might be provided and coupled to the pump working chamber. Anoutlet might be coupled to the pump working chamber for outletting theliquid at the high pressure. Such outlet might comprise an outlet valveadapted to permit liquid flow only unidirectional. An inlet might becoupled to the pump working chamber for inletting the liquid into thepump working chamber. The pressure of the liquid at the inlet is usuallylower than the pressure at which the pumping apparatus outputs theliquid. The inlet might comprise an inlet valve to permit liquid flowonly unidirectional.

The outlet valve and/or the inlet valve might be embodied by or comprisea check valve, active valves, rotary slide valves, or any other valve asknown in the art adapted to ensure unidirectional flow of the liquid.

The piston can be provided using any kind of suitable material. Typicalrequirements in embodiments might be to provide one or more of thefollowing: sufficient hardness (in particular to reduce abrasion),sufficiently durability (e.g. chemically inert) in particular againstchemical solvents e.g. as used in chromatography, sufficient surfacequality in particular to ensure sufficient sealing, long life time, etc.Embodiments of the piston might comprise at least one of the followingmaterials: hard metal (e.g. carbide, tungsten carbide WC, etc.), ceramicmaterials (such as ZrO2, Al2O3, TiC, SSiC, Si3N4, etc.), stainless steel(in particular temperable stainless steel), titanium, etc.

The piston might be at least partially coated, e.g. with a diamond-likecarbon coating, adapted to provide a reduced abrasion of the piston,e.g. against the drive seal and/or the pump working chamber. Theteaching of the European Patent application 06117516.2, by the sameapplicant, with respect to such coating shall be incorporated hereby byreference.

The drive might comprise a spindle drive mechanism as described indetail in the aforementioned EP 309596 A1, the teaching thereof withrespect to the drive mechanism shall be incorporated herein byreference. Other couplings might comprise one or more of a cam disc, agear drive, etc.

The return mechanism might comprise at least one of a spring, ahydraulic cylinder, a drive mechanism, a deflection mechanism, as knownin the art. Alternative, a separate drive might be used which is tensionforced coupled to the piston and couples from an opposite direction asthe drive. In one embodiment, a return rod is coupled between the pistonand the return mechanism. The rod and the piston might be provided asone piece, or might be coupled to each other using force or formcoupling as known in the art.

In one embodiment, the pumping apparatus is coupled with another pumpingapparatus, whereby both pumping apparatuses might be embodied in thesame way but may also be different. Providing two pumping apparatusesallows to provide an essentially continuous liquid flow, as well knownin the art and also explained in detail in the aforementioned EP 309596A1. Such so called dual pump might comprise the two pumping apparatusesin either a serial or a parallel manner. In the serial manner, asdisclosed in the aforementioned EP 309596 A1, the outlet of one pumpingapparatus is coupled to the inlet of the other pumping apparatus. Theteaching in the EP 309596 A1 with respect to the operation andembodiment of such serial dual pump shall be incorporated herein byreference.

In the parallel manner, the inlets and the outlets, respectively, ofboth pumping apparatuses are coupled together.

In both manners, serial and parallel, operation of the two pumpingapparatuses is phase shifted, usually by about 180 degrees. The phaseshifting might be varied in order to compensate pulsation in the flow ofliquid as resulting from the compressibility of the liquid.

Embodiments of the afore described pumping apparatus might be applied ina liquid separation system comprising a separating device, such as achromatographic column, having a stationary phase for separatingcompounds of a sample liquid in a mobile phase. The mobile phase is thendriven by the pump. Such separation system might further comprise atleast one of a sampling unit for introducing the sample fluid into themobile phase, a detector for detecting separated compounds of the samplefluid, a fractionating unit for outputting separated compounds of thesample fluid, or any other device or unit applied in such liquidseparation systems.

Embodiments of the invention can be partly or entirely supported by oneor more suitable software programs, which can be stored on or otherwiseprovided by any kind of data carrier, and which might be executed in orby any suitable data processing unit.

BRIEF DESCRIPTION OF DRAWINGS

Other objects and many of the attendant advantages of embodiments of thepresent invention will be readily appreciated and become betterunderstood by reference to the following more detailed description ofembodiments in connection with the accompanied drawing(s). Features thatare substantially or functionally equal or similar will be referred toby the same reference sign(s).

FIG. 1 illustrates a typical example of a pump 10 as known in the art.

FIGS. 2 and 3 show exemplary embodiments of a pumping apparatus 200according to the present invention.

FIG. 4 a shows an embodiment of a serial dual pump, and FIG. 4 b showsan embodiment of a parallel dual pump.

FIG. 5 shows a liquid separation system 500.

In FIG. 2, as also illustrated with respect to FIG. 1, the piston 20reciprocates in opposing directions in the pump working chamber 30.However, whereas in FIG. 1 the drive 40 is pressure force coupled to thepiston 20 and “pushes” the piston 20 into the pump working chamber 30 inorder to reduce the pump volume 60, the drive 40 in FIG. 2 is tensionforce coupled to the piston 20 and applies a tension force onto thepiston 20 in order to “draw/pull” the piston 20 into the direction 50was increasing the pump volume.

An input valve 70 might be provided in order to ensure that liquidprovided at the input 20 (as received e.g. from a liquid reservoir oranother pump, as indicated by reference numeral 130) can flow onlyunidirectional into the pump working chamber but not in return.

An outlet valve 80 might be provided at the outlet 110 of the pumpingapparatus 200 in order to ensure unidirectional flow of the liquid fromthe pump working chamber into the system as coupled to the pumpingapparatus 200.

The piston 20 is preferably sealed by the drive seal 90 in order toretain the liquid in the pump volume 60. In the embodiment of FIG. 2, areturn seal 210 is provided in order to seal the pump volume 60 againsta return rod 230 coupled to the return mechanism 100. The returnmechanism 100 is provided to move the piston 20 into a return direction220 opposite to the drive direction 50.

The application of force coupling between the piston 20 and the drive40, as in embodiments of the present invention, reduces the requirementfor lateral guidance of the piston 20, thus leading to a less complexand usually less costly design together with a reduced abrasion inparticularly for the sealing.

FIG. 3 shows another exemplarily embodiment of the pumping apparatus 200in greater technical detail. The return mechanism 100 is embodied hereby a spring.

In the serial dual pump of FIG. 4 a, a first pumping apparatus 200A iscoupled at is input to a liquid supply (not shown), and its output iscoupled to the input of a second pumping apparatus 200B. At least oneand preferably both of the pumping apparatuses 200A and 200B areembodied in accordance with the aforementioned embodiments. In order toprovide a continuous flow of liquid, the pump volume of the firstpumping apparatus 200A might be embodied to be twice of the pump volumeof the second pumping apparatus 200B, so that the first pumpingapparatus 200A will supply a portion of its pump volume directly intothe system and the remaining portion to supply the second pumpingapparatus 200B, which will then supply the system during the intakephase of the first pumping apparatus 200A. The ratio of the pump volumeof the first pumping apparatus 200A to the second pump operatives 200Bis preferably 2:1, but any other meaningful ratio might be appliedaccordingly. Further details of the operation mode of such dual serialpump are disclosed in the aforementioned EP 309596 A1 and shall beincorporated herein by reference.

In the parallel dual pump of FIG. 4 b, the inputs of a first pumpingapparatus 210 and a second pumping apparatus 200D are coupled inparallel to the liquid supply 130, and the outputs of the two pumpingapparatuses 200C and 200D are coupled in parallel to the systemreceiving the liquid at high pressure. The two pumping apparatuses 200Cand 200D are operated usually with substantially 180 degree phase shift,so that only one pumping apparatus is supplying into the system whilethe other is intaking liquid from the supply 130. However, it is clearthat also both pumping apparatuses 200C and 200D might be operated inparallel (i.e. concurrently), at least during certain transitionalphases e.g. to provide a smooth(er) transition of the pumping cyclesbetween the pumping apparatuses.

FIG. 5 shows a liquid separation system 500. A pump 400, which might beembodied as illustrated in FIG. 4 a or 4 b, drives a mobile phasethrough a separating device 510 comprising a stationary phase. Asampling unit 520 is provided between the pump 400 and the separatingdevice 510 in order to introduce a sample fluid to the mobile phase. Thestationary phase of the separating device 510 is adapted for separatingcompounds of the sample liquid. A detector 530 is provided for detectingseparated compounds of the sample fluid. A fractionating unit 540 can beprovided for outputting separated compounds of sample fluid.

Further details of such liquid separated system 500 are disclosed withrespect to the Agilent 1200 Series Rapid Resolution LC system or theAgilent 1100 HPLC series, as both provided by the applicant AgilentTechnologies, under www.agilent.com which shall be in cooperated hereinby reference.

1. A pumping apparatus for delivering liquid at a high pressure at whichcompressibility of the liquid becomes noticeable, comprising a pistonadapted for reciprocation in opposing directions in a pump workingchamber, a drive coupled to the piston to apply a tension force onto thepiston in order to move the piston into a drive direction, and a returnmechanism, coupled to the piston, being adapted for counteractingagainst the movement of the piston into the drive direction and to applya tension force onto the piston in order to move the piston into areturn direction opposite to the drive direction, wherein the returnmechanism is coupled to a side of the piston facing into pump workingchamber.
 2. The pumping apparatus of claim 1, comprising at least oneof: a return seal adapted for sealing the pump working chamber against areturn mechanism counteracting against the movement of the piston; adrive seal adapted for sealing the pump working chamber against thedrive.
 3. The pumping apparatus of claim 1, comprising at least one of:a pump volume in the pump working chamber is increased when the pistonis moved into the drive direction; the pump volume in the pump workingchamber is decreased when the piston is moved into the return direction;a valve, coupled to the pump working chamber, to permit liquid flow onlyunidirectional; an outlet coupled to the pump working chamber foroutletting the liquid at the high pressure, wherein the outlet comprisesan outlet valve adapted to permit liquid flow only unidirectional; aninlet coupled to the pump working chamber for inletting the liquid at apressure lower than the high pressure at the outlet, wherein the inletcomprises an inlet valve adapted to permit liquid flow onlyunidirectional; the piston is at least partially coated with adiamond-like carbon coating adapted to provide a reduced abrasion of thepiston.
 4. The pumping apparatus of claim 1, wherein the drive comprisesat least one of: a spindle drive mechanism, a linear motor, a stepmotor; a driving rod coupled to the piston.
 5. The pumping apparatus ofclaim 1, wherein the return mechanism comprises at least one of: aspring, a hydraulic cylinder, a drive mechanism, a deflection mechanism,a drive tension-coupled to the piston; a return rod coupled to thepiston.
 6. A pump comprising a first pumping apparatus of claim 1, and asecond pumping apparatus of claim 1, wherein the first and the secondpumping apparatus are coupled either in a serial manner, with an outletof the first pumping apparatus being coupled to an inlet of the secondpumping apparatus, and an outlet of the second pumping apparatusproviding an outlet of the pump, or in a parallel manner, with an inletof the first pumping apparatus being coupled to an inlet of the secondpumping apparatus, and an outlet of the first pumping apparatus beingcoupled to an outlet of the second pumping apparatus, thus providing anoutlet of the pump; and a liquid outlet of the first pumping apparatusis phase shifted essentially 180 degrees, with respect to a liquidoutlet of the second pumping apparatus.
 7. A liquid separation system,comprising a separating device comprising a stationary phase forseparating compounds of a sample liquid in a mobile phase, and a pumpaccording to claim 6, adapted for driving a mobile phase through theseparating device.
 8. The separation system of claim 7, comprising atleast one of: a sampling unit adapted for introducing the sample fluidto the mobile phase, a detector adapted for detecting separatedcompounds of the sample fluid, a fractionating unit adapted foroutputting separated compounds of the sample fluid.
 9. A method ofdelivering a liquid at a high pressure at which compressibility of theliquid becomes noticeable, comprising reciprocating a piston in opposingdirections in a pump working chamber by applying a tension force ontothe piston in order to move the piston into a drive direction, wherein apump volume in the pump working chamber is increased when the piston ismoved into the drive direction, and counteracting against the movementof the piston into the drive direction by coupling to a side of thepiston facing into pump working chamber, thus applying a tension forceonto the piston in order to move the piston into a return directionopposite to the drive direction.
 10. A software program or product,stored on a data carrier, for controlling the method of claim 9, whenrun on a data processing system.